| How the forest growth in the future? Which method was suited for cultivating the forest to timber forest, public welfare forest or carbon sick forest? In which extent the climate or the environmental change could affect the forest growth? Forest scientists and forest managers wanted wishfully to find out the answers of all these questions. Forest growth model is an important tool for forecasting the forest development and the process-based model with climate, site and physiology factors was became the focus point in the model research scope. Hybrid model which could model the forest management measures and the tree physiological ecology growth processes in the same time was emerged as the times require.Process-based models forest growth simulation system FVS-BGC (Forest vegetation simulator & Bio-Geochemical Cycles) was studied in deeply level for building a FVS-BGC system for Beijing area with two experimental species Pinus tabulaeformis and Platycladus orientalis. The valuable experiences in this researching process could been very useful and set a strong foundation for building a regional or a nationwide FVS-BGC system. Four major conclusions in this study were in below part.(1) The system components, executive process and key growth models were analyzed. The system running needs five type data, tree-level data, stand-level data, climate data, site data and tree physiology data. Also, five output data of tree or stand level in daily or yearly growth and physiological ecology data could be predicted. Growth models were the mainly component of FVS-BGC, there are seven types experienced models includes DBH-H model, crown ratio model, crown width model, crown competition factor model, DBH model, height models and mortality model. There are six type physiological ecology modules in FVS-BGC, radiation module, water module, photosynthesis module, respiration module, stomatal conductance module and NPP module.(2) Key independent variables were researched and the mainly growth models were optimized rebuilt based on previous studies and the primary works included:1) rebuilt the site index table of Pinus tabulaeformis,2) built the height model of mean tree and the dominant tree, 3) built the crown competition factor model,4) rebuilt the stand density index model of Pinus tabulaeformis and Platycladus orientalis and figured out the maximum stand density index of the two species,5) rebuilt the DBH-H model, crown width model and DBH growth model. Correlation index was used for evaluating the model fitting effect and the results showed that all models had a highly predictive validity.(3) Three type parameters of FVS-BGC were determined which includes climate parameters, site parameters and tree physiology parameters. There are five climate parameters in daily level were maximum temperature, minimum temperature, relative humidity, precipitation, total radiation and transmissivity. Two methods of doing experiment and reading references were used for determining the site parameters and the tree physiology parameters. The maximum soil water content of 0-30cm and the absolutely water volume in four site types of Pinus tabulaeformis and Platycladus orientalis were determined by doing experiment. The maximum photosynthesis rate were 7μmol·m-2·s-1and 5pμmol·m-2·s-1, the maximum temperature and the optimum temperature were 25℃and 45℃, the specific leaf area were 11m2/kg and 17m2/kg, the crown extinction coefficient were 0.8 and 0.7 of Pinus tabulaeformis and Platycladus orientalis. The proportion of leaf, stem and root biomass in whole tree was 15%,17%,12% of Pinus tabulaeformis, for Platycladus orientalis the proportion was 15%,17% and 12% respectively. The carbon content rate of each organ set 0.5 forcibly.(4) The Beijing FVS-BGC was built based on above works.20 years with 5 yearly repetition measurement fixed plots'data were used for testing the FVS-BGC predicted values and results showed that predicted values were closed to the measured values. The predicted effect and system sensitivity were also tested with 4 typical plots,2 plots for each species, the predicted results showed that experience based values were exceeded the process based values with about 28% which most similar contrasted with other foreign studies. At last, we used FVS-BGC to simulated lower level thinning depended on DBH and upper layer thinning depended on Height with two highly density stands of Pinus tabulaeformis and Platycladus orientalis respectively with the target of selected the optimal forest management decision and we achieved the goal.In the new century, the hybrid model became the focus both in forest ecosystem modeling and forest management modeling scope. In this study, we analyzed the growth models in source code level, simulated the physiological ecology growth condition of Pinus tabulaeformis and Platycladus orientalis in both tree level and stand level, contrastive analyzed the predicted results of same object but with different model methods and researched the differences between experienced based model and the processed based model by using the FVS-BGC for the first time. This study provided a reference for building a regional or nationwide forest growth simulation system FVS-BGC and also has a valuable significance of theory and practice.
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